OBJECTIVE: To investigate the short- and long-term pathologic and physiologic effects of ionizing radiation on the liver. APPROACH: Screened, dewormed, vaccinated, quarantined dogs will be anesthesized and irradiation given to the liver. Phase I: To develop an LD80 model. Phase II: To manipulate time, dose and fractionation in whole liver irradiation. Phase III: To vary the liver volume irradiation (25-90 percent) and to give heparin to certain sub-groups. Parameters (pre-treatment and at 3-4 mo. intervals): physical examination, esophagoscopy, laparotomy, liver biopsy, portal manometry, liver scanning, liver functions. Analysis: ANOVA and correlation tests.